When do you use "is being" in English?

Solution 1:

"Is being" is used to describe an action that started in the past and continues at present. So these sentences have different meanings:

• "Something is changed" describes the state of something; it has changed, maybe recently, maybe a long time ago.
• "Something is being changed" describes the current event that is happening right now; it is changing.

Solution 2:

One of the uses is simple Present Continuous in passive voice.

My house is being painted by the workers

means exactly the same as

The workers are painting my house

Another is a bit more complicated. Is being may be used to indicate, that someone (rarely something) at the moment possess a quality that they may or may not possess in general.

My brother is being mean.

He may not be mean usually, but right now he is. I say complicated, because there are some instances, where is being is not used.

My wife is mad at me

She's not mad at me usually I hope, but she is mad now. Note, that is being is not used in this context.

Solution 3:

"Something is changed" would usually be used as part of a sentence looking to the future after the change: "When X is changed, we can do Y."

Used on its own, "something is changed" sounds a bit odd; we'd normally say "something is different" or "something has changed", which means the change has already taken place.

"Something is being changed" indicates the change is taking place right now; it's roughly the same as "Something is changing."